Skin is one of the largest organs in the body and covers substantially the entire body surface. Skin is composed of two main layers: the surface epithelium or epidermis which includes the uppermost stratum corneum, and the subjacent connective tissue layer or dermis. The skin has a number of functions such as protecting an organism from injury and dessication, receiving environmental stimuli, excreting various substances, regulating body temperature and helping to maintain water balance. Because of its quantitative and qualitative importance, substantially intact and healthy skin is crucial not only for the well being of an organism but for its very survival.
The health and integrity of skin may be compromised by wounds, abrasions, ulcers, burns, infections, irritations, premature birth and other conditions for which normal skin production and repair processes may be inadequate. For example, acute conditions such as patients who are burned over a large surface area often require immediate skin replacement. Less life-threatening but chronic skin problems such as decubitus ulcers or irritations from diaper rash may progress to more severe conditions if left untreated or if they occur in a neonate or a geriatric patient. Skin treatments encompass a variety of methods and products. These may range from symptomatic treatments such as the use of topical anti-inflammatory compounds to the use of replacement skin. For various physiological, medical, and other reasons, however, none of these treatments meet the desired goal of utilizing the body's own healing and repair system to promote its own skin growth and maturation.
Vernix caseosa (vernix) is a naturally occurring skin protectant. Vernix is a lipid rich substance composed of sebum, epidermal lipids, and desquamated epithelial cells that covers the skin of the developing fetus in utero while the fetus is completely surrounded by amniotic fluid. Vernix consists of hydrated cells dispersed in a lipid matrix. This lipid matrix undergoes a transition to a more fluid form at physiological temperatures and with the application of shear forces, such as those encountered with movement. Vernix is a covering for the skin of the fetus that resembles the stratum corneum except that it lacks multiple rigid desmosomal connections. Consequently, vernix exhibits a viscous fluid character.
The lipid component of vernix has been reported in Stewart et al., J. Invest. Dermatol, 78:291-295 (1982); Nicolaides, Lipids 6:901-905 (1972); Haahti et al., J. Clin. & Lab. Investigation, 13:70-73 (1961); Karkkainen et al., J. Invest. Dermatol, 44:333-338 (1965); and U.S. Pat. No. 5,631,012, each of which are incorporated by reference herein in their entirety. Lipids, defined herein as fats or fat-like substances, include lecithin and other phospholipids, squalene, waxes, wax esters, sterol esters, diol esters, triglycerides, free sterols and four classes of fatty acids ranging in chain length from C.sub.12 to C.sub.26 (straight chain saturated, straight chain unsaturated, branched chain saturated, and branched chain unsaturated).
Because of its anticipated skin maturation and protectant properties, vernix appears to have promise as a clinically effective therapeutic agent. Application of vernix to clinical use, however, has been limited by its physical properties. While vernix in utero is a tractable semi-solid, vernix ex utero is a nonhomogeneous intractable compound with a consistency comparable to cheese or hardened cake frosting. Vernix is not completely soluble in conventional solvents such as absolute ethanol, 95% ethanol, 2-propanol, and combinations of chloroform and methanol. Thus, controlled and uniform administration of vernix to a surface is difficult. While it has been reported that the surfactant polysorbate 80 (Tween 80) may solubilize vernix, Tween 80 is toxic to living cells and therefore cannot be used clinically. While there have been isolated reports of vernix directly scraped from a newborn baby for smearing over wounds (SU Patent No. 1718947A) or in an artificial lipid composition for use as a cosmetic moisturizer (U.S. Pat. No. 5,631,012), vernix in a therapeutic or prophylactic composition has not yet been reported.
While the barrier function and skin growth and maturational properties of vernix render it clinically useful to treat a variety of acute and chronic conditions, its physical properties have heretofore prevented its controlled administration in a clinical environment for therapeutic or prophylactic use. A need thus exists for a clinically useful vernix formulation.